This invention relates to a static mixer apparatus for mixing viscous fluids which is constructed from an inner housing which has an inlet for material to be mixed and an outlet for material to be mixed and which comprises two or more layers of undulating or zigzag bars which are parallel to each other and which are disposed one above another rotated by an angle .alpha., preferably of 90.degree., to each other in an alternating manner and which are joined to each other at their upper or lower vertices. The bars are provided in particular with channels for the passage of a heat transfer fluid so that the mixer can also be employed as a heat exchanger.
Static mixers are often employed as built-in components for the mixing of liquids in pipelines. A pump pushes the liquids to be mixed through a pipe which is provided with built-in components such as these.
The two following apparatuses can be cited as examples of static mixers.
In what are termed Kenics mixers (see "Mischen beim Herstellen und Verarbeiten von Kunststoffen", published by: VDI-Ges. Kunststofftechnik. VDI-Verlag Dusseldorf, 1986, pages 238-241) the flow of fluid is divided by a separator plate installed in the pipe. This plate is twisted about the pipe axis. A swirling flow occurs in each of the two partial flows of liquid, and results in the redistribution of the liquid over the cross-section thereof. In practice, there is a plurality of mixing elements such as this disposed in series in order to divide the liquid again and again and to achieve a good mixing effect. The stability under pressure of these mixers when employed for highly viscous fluids is comparatively low.
What are termed SMX mixers (see U.S. Pat. No. 4,062,524) consist of two mutually perpendicular grids of parallel sheet metal strips which are welded to each other at their points of intersection. On account of the many weld joints, the production cost of these mixers is relatively high.
The exchange of heat from or to highly viscous liquids during their passage through known heat exchangers typically occurs at a very low Reynolds number. If plain tubes are used for the exchange of heat, for example, the rate of exchange of heat is low at a Reynolds number which tends to zero, and on the heat exchanger side depends substantially only on the length of tube used. It is possible to achieve a significant improvement in the exchange of heat by combining a tubular heat exchanger with a static mixer device.
This combination is known in two embodiments. Firstly, static mixer elements can be inserted in the tubes of a tube bundle heat exchanger. The aforementioned Kenics mixer elements are used in particular here. Secondly, the tubes can be employed as elements of a static mixer. This is described in German Patent Specification DE 28 39 564 C2, for example.
The use of a tube bundle heat exchanger through which a product flows has to be rejected for many chemical processes, however. For example, if a polymerisation reaction has to be cooled, a higher degree of polymerisation is obtained in a tube through which slow flow occurs, due to the increased dwell time of the reactants. The liquid in the tube thereby possibly becomes more viscous than that in adjacent tubes. As a consequence, the velocity of flow of the material to be mixed is further reduced. For a given set of process parameters, the tube can therefore become blocked by polymer.
In processes such as these, a static mixer is preferred which is formed from heat exchanger tubes, such as that described in DE 28 39 564 C2. However, the production cost of these mixers is so high that this solution is frequently rejected as being uneconomic.